# Symmetrical component equation question.

Discussion in 'General Electronics Chat' started by mbohuntr, Oct 25, 2010.

1. ### mbohuntr Thread Starter Active Member

Apr 6, 2009
413
32
I may be taking a class in protective relaying soon, and need to get a jump on the math since I'm no engineer. The attached link shows Fortesque's theory in matrix form on page(s) 2 and 3. If anyone has the time, could they do a calculation using imaginary voltages? I am beginning to understand the "a" operator, but maybe if someone were to write out a complete calculation using TEX, I would grasp it easier. (I tried TEX, and haven't got it yet.) I do understand the concept of positive, negative and zero sequences, I just can't seem to put it together in any coherent fashion. (The equation doesn't have to follow the matrix method, It might be easier to calculate individual phases like the middle of page three.) I guess I don't understand the process or the goal. Thanks a LOT, this will be a lot of work. Mike

http://www.ece.umd.edu/class/enee474.F2003/PDF%20Files/chp10_1.pdf

Last edited: Oct 25, 2010
2. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
I'm not clear on what you want.

Do you require a worked example of how you get from the unbalanced 3-phase set to the symmetrical component equivalent set? Surely that's what the (attached) document writer has already attempted to demonstrate.

What's the relevance of your requirement to have it written in TEX?

3. ### mbohuntr Thread Starter Active Member

Apr 6, 2009
413
32
Yes, for some reason I can't wrap my head around the process as well as the result. I understand adding the zero sequence component vectors to obtain zero current on the neutral, but I am not clear on what to do with unbalanced components. I figured if someone came up with some imaginary phase voltages, and worked the problem, it would become clear to me. No, this isn't homework, I already graduated. My math skills are weak when equations are concerned. Thanks, Mike (It doesn't have to be in TEX, but that comes out the clearest. )

4. ### subtech Senior Member

Nov 21, 2006
123
5
I may be too late in getting here...

I can't help with the matrix math, but I can walk you through a practical example using simple numbers. If that would help you, post again and we'll give it a go.

Mke

5. ### mbohuntr Thread Starter Active Member

Apr 6, 2009
413
32
Absolutely! Understanding the goal would be just as good as the traditional approach. I work in a generating station, and would like to bid into a better job. Protective relaying seems to be the gold ring as far as training goes, so if I get that, it would make the resume shine... Thanks.

6. ### subtech Senior Member

Nov 21, 2006
123
5
Okay then. I'm glad you told me you work in a power plant. We will proceed using examples that are specific to devices found in a power plant.
I'm going to do this in stages because my time is limited due to my work situation at the moment. Also, I'm not familiar with TeX, but I'm willing to try it. If you've got the patience to wait on me, I'll do my best.

Note: Relay technicians are well trained because they MUST be. Making mistakes when working on relays that protect large generators is very, very bad.

Have you had any classes/training with symmetrical components, or are you studying on your own?

Mike

7. ### mbohuntr Thread Starter Active Member

Apr 6, 2009
413
32
Thanks! I just finished my AAS in electrical technology last spring. I am doing this on my own right now, there are several classes each year offering certificates in relaying, but I'm worried the pace will be too fast unless I get a jump on the math. It would by fine if you wrote the work down and scanned it. Tex seems to be easier online if you are used to it.

I don't understand the applications of positive and negative sequence calculations. I don't see why you cannot simply take a reading with a meter for each phase, and calculate the neutral current??? If you take a reading of 240v,240v,170v, Then you can break down the instantaineous voltages by the 3 vectors, but what good does this do you?? you already know you have a fault on the third phase??? What am I missing here???

If you wish, you can PM me with the stuff. The mods here are really great about sharing the knowledge publicly here, I just don't know if the general population is gonna want to read this stuff.

Last edited: Oct 28, 2010